A disc brake of the afore-described type is taught, for example, by DE-OS 29 31 071. In the state-of-the-art disc brake, a wire spring bent in S-type manner is located in the center of the brake. The ends of the wire spring are in abutment with the back plates of the brake shoes, thereby preloading the brake shoes in the brake releasing direction. One end of the wire spring is secured to a piston-sided brake shoe. The wire spring, hence, is "floatingly" arranged rather than secured to a stationary point of fixation.
With an increasing wear of the friction pads, the floating caliper will displace along with the outer brake shoe disposed opposite the actuator while the piston-sided brake shoe in abutment with the actuator will displace relative to the floating frame and to, the expander spring, by an amount corresponding to the aggregate of the two worn friction pad strengths. In view of the non-symmetrical arrangement of floating caliper-type disc brakes relative to the displacement paths of the brake shoes, a "floating" expander spring does not always ensure, after braking, a uniform distribution of the brake clearance among the two brake shoes.
Moreover, electrical indicators for displaying the pad wear of the brake pads are known in the art. Such indicators comprise, for example, an electrical contact provided on the brake pad, which with a pad increasingly worn, is closed or discontinued. However, an indicator of this type is suitable only to warn against worn-out brake pads rather than to continuously display the pad strength. Other means suitable for a continuous display make use, for example, of the displacement of the brake caliper vis-a-vis the brake carrier firmly anchored to the steering knuckle of the vehicle, which grows with an increasing pad wear. For this purpose, usually, a variable electrical resistor having a displaceable slider is used. The disadvantage involved with the latter means resides in the relatively complex design thereof causing rather high manufacturing costs.
It is the object of the invention to provide a floating caliper disc brake having uniform distribution of the brake clearance among the brake shoes.
Another object of the invention is to provide a low-cost electrical pad wear indicator.